you have a buffer system made up of equimolar amounts of carbonic acid, H_2OCO_3

Question

you have a buffer system made up of equimolar amounts of carbonic acid, H_2OCO_3, and sodium bicarbonate, NaHCO_3. Write equations to show how this buffer behaves when HCl is added and NaOH is added. Calculate the expected pH values of the buffer systems from the experiments (a, b, c, d), using the Henderson-Hasselbalch equation shown in the Background section. Use tor pK_a values: carbonic acid = 6.37 and acetic acid = 4.75. Are these calculated values in agreement with your measured pH values?

Explanation / Answer

Q4.

H2CO3 and NAHCO3 buffer

thi is:

H2CO3 <--> H+ HCO3- system

pKa1 = 6.37

write equations for:

a) addition of HCl

HCl --> H+ + Cl- since it is strong

so

H2CO3 <--> H+ HCO3-

the shift goes toward more H2CO3 production... so

H+(aq) + HCO3-(aq) --> H2CO3(aq)

for

b) NaOH addition

NaOH --> Na+ + OH-

OH- reacts with H+ ions to form H2O(l)

so the shift:

H2CO3 <--> H+ HCO3-

goes toward more H+ and HCO3- production

NaOH(aq) + H2CO3 <--> H2O(l) + Na2CO3 + HCO3-

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